Reduce type equality check within symex

Once all the cases are fixed, this can be returned to a regular equality

Author: thk123

src/goto-symex/symex_assign.cpp

@@ -29,7 +29,8 @@ void goto_symext::symex_assign(
   exprt rhs=code.rhs();
 
   DATA_INVARIANT(
-    lhs.type() == rhs.type(), "assignments must be type consistent");
+    base_type_eq(lhs.type(), rhs.type(), ns),
+    "assignments must be type consistent");
 
   clean_expr(lhs, state, true);
   clean_expr(rhs, state, false);